The invention resides in an apparatus for the electrographic printing and copying using liquid coloring agents, including a latent image carrier and a supply element having at least one slot-like supply nozzle via which the liquid coloring agent can be applied to the latent image carrier and a suction element for the removal of excess coloring agent from the latent image carrier.
Such an apparatus is known for example from GB 2 243 227 A. In this apparatus, liquid toner is applied to a latent image carrier in the form of an imaging drum. To this end, the apparatus includes a slot-like outlet via which liquid toner, pressurized by means of a pump is applied to the imaging drum. In the movement direction of the imaging drum behind the slot-like outlet, a slot-like inlet is arranged to which a vacuum is applied. In this way, toner which does not adhere to the imaging drum is sucked off the imaging drum. Between the outlet and the inlet, an electrode is arranged at a small distance from the surface of the imaging drum.
Since the inlet is arranged, in the direction of movement of the imaging drum, a small distance after the electrode, toner which is blocked by the electrode cannot be removed by the inlet. Although an excess passage is disposed, in the direction of movement of the imaging drum, before the outlet, only toner which is disposed at the side of the outlet remote from the electrode reaches the excess passage. Toner which adheres to the imaging drum cannot be taken up by the excess passage.
DE 32 30 862 A1 discloses an apparatus wherein, for the development of a charge image which is applied to an electrically coated image carrier, the image carrier is wetted by a liquid developer or, respectively, a coloring agent from a dispersing device or, respectively, by a carrier liquid and toner particles. By means of the charge image, a part of the toner adheres to the surface of the image carrier in the form of an image. The remaining toner is removed to prevent background coloring. Furthermore, dispersant is removed from the image carrier such that only so much dispersant remains on the image carrier that the developed charge picture can be properly and rapidly further treated. To this end, a removal member is provided which is moved relatively to the image carrier and whose surface is only very slightly immersed into the liquid developer disposed on the image carrier, so that part of the dispersant contained in the liquid developer is removed for example by adhesion. Furthermore, an electric field is applied between the removal device and the image carrier, whose field direction depends on the charge of the toner contained in the liquid developer. By this electric field, the toner which is not attached in the form of an image is removed by the removal device.
In the known apparatus, the liquid developer is applied to the image carrier by means of a separate element which is spatially separated from the removal device. Since also this element must be arranged at a correct distance from the image carrier, it is necessary to separately adjust the distance of the element from the image carrier and the distance of the removal device from the image carrier wherein particularly the distance of the removal device from the image carrier must be adjusted very accurately. This distance determines whether unnecessary toner or, respectively, excessive dispersant is removed from the image carrier with sufficient thoroughness.
DE 100 27 173 A1 further discloses an apparatus and a method for the electrographic printing and copying using liquid coloring agents which generally consist of a carrier fluid and toner particles. The apparatus includes an applicator element which carries a layer of a coloring agent. Between the liquid layer and the opposite surface of the latent image carrier, there is an air gap. For the coloring of the latent image on the image carrier, droplets are transferred from the liquid layer to the surface of the latent image carrier through the air gap. In this way, the latent image is inked so as to form a coloring agent image. This coloring agent image can then be transferred directly to a final image carrier which may consist for example of paper.
The apparatus may also include a cleaning station in which the latent image carrier is cleaned after the transfer of the coloring agent image that is, the residual carrier and a well-defined initial state is re-established. The cleaning station may include a suction device which sucks off the residual liquid coloring agents from the surface of the image carrier. The discharge air may be filtered and the liquid coloring agent may be precipitated for reuse in a later printing process.
U.S. Pat. No. 6,385,421 B1 discloses a printing apparatus which includes a latent image carrier in the form of an imaging drum. At the imaging drum, four development units are arranged by means of which liquid tones of different colors are applied to the imaging drum. The toner is applied by means of transfer drums which immerge on one hand into a reservoir which includes liquid toner and, on the other hand, come in contact with the surface of the latent image carrier.
In the direction of movement of the imaging drums behind the transfer drums, there is in each case a vacuum nozzle by way of which excess liquid toner is removed from the latent image carrier. With the use of drums for the transfer of the liquid toner to the latent image carrier however high printing speeds cannot be achieved.
EP 0 223 693 A2 finally discloses a plotter-toner station for an electrostatic printer which comprises a printing head and a developer unit attached to the printing head. By means of the printing head, a charge is applied to a final image carrier which typically consists of paper and which passes by the printing head. Following the printing head, the final image carrier passes the developer unit. The developer unit includes a drum by way of which toner is applied to the final image carrier. To this end, liquid toner is sprayed earlier onto the drum.
After the toner has been applied to the drum, the final image carrier passes by a vacuum chamber by means of which excess liquid toner is removed from the final image carrier. To this end, the vacuum chamber has openings via which toner disposed in areas of the final image carrier which are not provided with a charge, is sucked off the final image carrier.
With the transfer of the toner by a drum to the image carrier however no high printing speed can be achieved.
It is the object of the present invention to provide an apparatus for the electrographic printing and copying using liquid coloring agents, with which a high printing speed can be achieved and which requires a small apparatus height.